Techniques for forming electrostatic image areas on dielectric surfaces are known. See, for example, U.S. Pat. No. 3,441,437. In these processes, electrodes (either fixed or movable) are utilized to deposit an electrostatic charge on a dielectric surface in a desired image pattern. The image pattern is then contacted with a developer composition brought into proximity to the image pattern by a magnetic development roll. The resulting developed image areas are subsequently subjected to heat, pressure, or heat and pressure to provide an essentially permanent image on the substrate.
During image formation an undesirable surface potential is applied to the dielectric surface in background (non-image) areas. Typically this surface potential is sufficient to attract enough of the developer composition to the background aras during the development step to give them undesirable coloration.
This background coloration may be reduced by applying a bias potential to the surface of the development roll which is equal to the surface potential of the background areas on the dielectric surface. However, it is very difficult to apply the appropriate bias potential to the development roll because the surface potential of the background areas varies on a given dielectric surface. Additionally, applying a bias potential adds to the complexity, size, and power requirements of electrostatic printing devices.
While many developer compositions are known, none has been found to provide the unique capabilities of the compositions of the invention. Thus, the present invention provides a composition which provides dramatically reduced background coloration when used in electrostatic printing processes that employ dielectric surfaces. Furthermore, the composition of the invention eliminates the need for applying a bias potential to the surface of the development roll.